A uniformly charged circular arc AB is of radius R covers a quarter of a circle and is located in the second quadrant. The total charge on the arc is Q > 0. This problem has 4 parts, I got the first 2. 1. The direction of the electric field E due to the charge distribution at the origin is in quadrant 4. 2. Determine [tex] \Delta E_x [/tex], the x-component of the electric field vector at the origin O due to the charge element [tex] \Delta q [/tex] locate at an angle [tex] \theta [/tex] subtended by an angular interval [tex]\theta [/tex]. [tex] \Delta E_x = kQ/R^2 * 2\Delta \theta / \pi * cos \theta [/tex] 3. Find E_x, the electric field at the origin due to the full arc length for the case where Q= 2.3 [tex]\mu C[/tex] and R= 0.37 m. Answer in units of N/C. I have no idea how to find the value for theta. Can someone tell me what I should do?